docs: def confirm_key(name, confirm_name, trafaret):
      """
      confirm_key - takes `name`, `confirm_name` and `trafaret`.
  
      Checks if data['name'] equals data['confirm_name'] and both
      are valid against `trafaret`.
      """
      def check_(value):
          first, second = None, None
          if name in value:
              first = value[name]
          else:
              yield name, t.DataError('is required'), (name,)
          if confirm_name in value:
              second = value[confirm_name]
          else:
              yield confirm_name, t.DataError('is required'), (confirm_name,)
          if not (first and second):
              return
          yield name, t.catch_error(trafaret, first), (name,)
          yield confirm_name, t.catch_error(trafaret, second), (confirm_name,)
          if first != second:
              yield confirm_name, t.DataError('must be equal to {}'.format(name)), (confirm_name,)
      return check_